Background: When well implemented, recess is a critical part of the school day for children's healthy development. We explored the implementation of a recess improvement process in 5 elementary schools across 3 states. Methods: We conducted a mixed-methods implementation study in which we visited each school 3 times over 1 school year, collecting observational, interview, survey, and focus group data. Qualitative data were coded thematically and analyzed across schools. Quantitative data were tabulated and aggregated over time and across schools. Results: We observed improvements in aspects of recess quality at each school, with three schools demonstrating the most progress. Quantitative data showed null effects in aggregate; however one school demonstrated significant improvements. Four criteria contributed to the quality and sustainability of recess reform: staff engagement, integration with other programs, student leadership, and recess communications. Implications for School Health Policy, Practice, and Equity: Program implementation research often refers to "buy-in" as a key ingredient to successful adoption. We provide a tool that helps to operationalize buy-in in the recess context. Conclusions: Changing the recess environment requires individual and institutional commitment to valuing recess as an important learning environment. School administrators must lead the change process and create institutional infrastructure to support success.